1 The basic unit of mass adopted under the System International d'Unites (10)
6 "Beware the ____ of March!" [Shakespeare] (4)
9 Motorway in Italy (10)
10 Car that runs on rails and is propelled by electricity (4)
13 US state, capital Atlanta (7)
15 Stephenson's ---, locomotive which attained 29 m.p.h. in 1829 (6)
16 Gas used in heating (6)
17 One who studies 18 across (15)
18 Ammonite or trilobite, for example (6)
20 An abnormal absorption with the self marked by communication disorders and short attention span and inability to treat others as people (6)
21 Complex carbohydrate found in many plants and used as a sweetening agent (7)
22 Mormon State (4)
25 Public declarations of intentions issued by a political party (10)
26 One of four playing cards in a deck having three pips (4)
27 Temperature scale that registers the freezing point of water as 32 degrees (10)

1 Ku-Klux --- (4)
2 Old stringed instrument (4)
3 Ring for packing pistons or sealing a pipe joint (6)
4 The Ark Royal was a famous one (8,7)
5 Vein in the centre of a leaf (6)
7 Skin disease (10)
8 Gershwin song (10)
11 Large yellow fruit, Citrus paradisi, with somewhat acid juicy pulp (10)
12 Bun filled with dry fruit (6,4)
13 The first book of the Old Testament (7)
14 Device that displays words for people to read on tv (7)
19 Capital of Zambia (6)
20 To the rear of the vessel (6)
23 Hordeolum, eye infection (4)
24 Interjection used to catch someone's attention (4)