This is the first time I've failed to find a word in both dictionaries and Google search: the only hit Google finds is the article where this quote appears:
「本間さんは頭脳頗る明晰、今後優良の成績で卒業される事となつた、卒業論文は『粉病菌科の分生胞子に就て』と言ふのでウドン粉病胞子のピプロシン体と称する貯蔵物質の化学的成分に関する学術的研究でなか〳〵立派なものだ」
I looked at the Japanese Wikipedia pages on うどんこ病 and 分生子 but I could not find any clues. I know that a 分生胞子 (conidium) can be "pip-shaped." Could that have any relation to 「ピプロシン」?
My translation of this sentence so far is:
Honma has an extremely lucid mind and is graduating with high grades; her graduation thesis on Conidium of Powdery Mildew is admirable academic research referring to ピプロシン体 as the chemical building blocks of storage material.
Thank you for any help you can provide!